Could this represent a good business model for a small store with an online only presence?
No imo it's forcing all of your customers to use bitcoin just so they could buy your product/service and it can be costly on the fee's if you're looking to spend $10 or less in every transaction. Having a wide range of payment method is better than limiting it to one because it can encourage sales and gives more options to your customers.
Are there any such retailers? All I can think of is illegal black market online stuff. You're probably going to find a few if you start browsing the dark web lol.
h0lybyte already mentioned a couple of them.